Conventionally, as methods for producing a cyanate ester compound, a method of allowing a cyanogen halide to react with phenol in the presence of a tertiary amine, a method of allowing a cyanogen halide to react with an alcoholic or phenolic alkaline metal salt, and the like have been known. In addition, it has been known that a cyanogen halide obtained by reacting hydrogen cyanide and/or a metal cyanide with halogen is used to produce a cyanate ester compound.
It has been proposed that, when hydrogen cyanide is reacted with chlorine in a water solvent or when sodium cyanide is reacted with chlorine in an aqueous solution of hydrochloric acid, so as to produce a cyanogen chloride, it is desired to terminate the reaction, such that unreacted hydrogen cyanide (unreacted sodium cyanide) or unreacted chlorine is not allowed to remain in the cyanogen chloride-containing solution, from the viewpoint of the safety of the cyanogen chloride (see, for example, Patent Literatures 1 and 2). However, it is extremely difficult to control the reaction such that neither unreacted hydrogen cyanide (unreacted sodium cyanide) nor unreacted chlorine remains in the reaction system, in order to terminate the reaction.
Moreover, when an aqueous solution of metal cyanide is allowed to react with chlorine in a halogenated hydrocarbon to produce a cyanogen chloride, it has been proposed to use the metal cyanide in an equimolar ratio of the chlorine, or less. For instance, it has been proposed that the molar ratio between a metal cyanide and chlorine is set from 1:1.15 to 1:1 (see, for example, Patent Literatures 3, 4, and 5).
Furthermore, when hydrogen cyanide or a metal cyanide is allowed to react with halogen to produce a cyanogen halide, even if the amounts of the hydrogen cyanide or the metal cyanide and the halogen used (the composition of the added materials) have been determined, the composition of a cyanogen halide-containing solution upon termination of the reaction (the generated cyanogen halide, unreacted halogen, unreacted hydrogen cyanide, unreacted metal cyanide) has not been determined (see, for example, Patent Literatures 1, 2, 3, and 4).
The thus produced cyanate ester compound generates a triazine ring as a result of hardening, and because of high heat resistance and excellent electrical properties, the cyanate ester compound has been widely used as a raw material for various functional polymer materials such as printed circuit boards, sealing materials for electronic components, molding materials, structural composite materials, adhesives, electrical insulating materials, and electrical and electronic components. However, in recent years, with the advancement of performance required in these application fields, various physical properties required for the cyanate ester compound as a functional polymer material have been increased. Examples of such physical properties required include flame retardance, heat resistance, a low coefficiency of thermal expansion, low water-absorbing property, low dielectric constant, low dielectric loss tangent, weather resistance, chemical resistance, and high fracture toughness. Nevertheless, to date, these required performances have not been necessarily satisfied.
For instance, in the field of semiconductor packaging materials, there is a problem that warpage occurs between a semiconductor chip and a substrate material due to a mismatch in coefficiencys of thermal expansion, with the thinning of the substrate. As a means for solving this problem, it has been desired to reduce the coefficiency of thermal expansion of a functional polymer material used as a substrate material and to improve high heat resistance. In addition, from the viewpoint of consideration on human bodies and environment, the use of lead-free solder has been promoted for the soldering of a printed wiring board. Also, from the viewpoint of resistance to a reflow step at a high temperature attended with the lead-free soldering, it has been desired to reduce the coefficiency of thermal expansion of a functional polymer material and to improve high heat resistance.
Moreover, it has also been desired to exclude halogen atoms that are likely to generate halogen gas having a risk of causing environmental contamination during combustion and are also likely to reduce the insulating property of a final product, or phosphorus atoms that are likely to reduce required physical properties other than flame retardance (i.e., heat resistance, moisture resistance, low water-absorbing property, etc.), and to improve the flame retardance of a functional polymer material.
As a simple cyanate ester compound, which is used to produce a hardened product having low thermal expansion and heat resistance, a difunctional cyanatophenyl-based cyanate ester compound (1,1-bis(4-cyanatophenyl)isobutane), in which the hydrogen in a methylene group binding cyanatophenyl groups is replaced by a specific alkyl group, has been proposed (see, for example, Patent Literature 6).
Furthermore, as simple cyanate ester compounds, which are used to produce hardened products having heat resistance and flame retardance, a cyanate ester compound having an aralkyl structure (see, for example, Patent Literature 7), a cyanate ester compound containing an isocyanuric acid skeleton (see Patent Literature 8), a cyanate ester compound containing a triazine skeleton (see, for example, Patent Literature 9), and a difunctional cyanatophenyl-based cyanate ester compound, in which the hydrogen in a methylene group binding cyanatophenyl groups is replaced by a biphenyl group (see, for example, Patent Literature 10), have been proposed. Further, as a mixture of cyanate ester compounds, which is used to produce a hardened product having heat resistance and flame retardance, a combination of a bisphenol A-based cyanate ester compound with a cyanate ester compound containing an imide skeleton (see, for example, Patent Literature 11) has been proposed.
On the other hand, such a cyanate ester compound has been conventionally used as a resin for printed wiring boards with excellent heat resistance. In recent years, high integration and/or miniaturization of semiconductors that are widely used for electronic devices, communication devices, personal computers and the like have been increasingly accelerated. With such high integration and/or miniaturization, laminates for semiconductor packaging, which are used for printed wiring boards, are required to have physical properties at high levels, such as heat resistance, low water-absorbing property, heat resistance upon moisture absorption, and flame retardance.
Examples of a cyanate ester compound widely used as a raw material for printed wiring boards and the like include a bisphenol A-based cyanate ester compound and a resin composition comprising another thermosetting resin or the like. The bisphenol A-based cyanate ester compound has excellent properties such as electrical properties, mechanical properties, and chemical resistance. However, in some cases, this compound is insufficient in terms of low water-absorbing property, heat resistance upon moisture absorption, and flame retardance. Hence, for the purpose of further improving such properties, studies regarding various cyanate ester compounds having different structures have been conducted.
As a resin having a structure that is different from that of the bisphenol A-based cyanate ester compound, a novolac-based cyanate ester compound has been frequently used (see Patent Literature 12). Moreover, prepolymerization of a novolac-based cyanate ester compound and a bisphenol A-based cyanate ester compound has been proposed (see Patent Literature 13).
Furthermore, as a method of improving flame retardance, it has been proposed to use a fluorinated cyanate ester compound, or to mix a cyanate ester compound with a halogen compound or prepolymerize these compounds, so as to allow a resin composition to comprise the halogen compound (see Patent Literatures 14 and 15).